Photographic silver halide transfer process and the print-receiving products useful in connection therewith



Feb. 11, 1958 E. H. LAND 2,823,122

PHOTQGRAPHIC SILVER HALIDE TRANSFER PROCESS AND THE I PRINT-RECEIVING PRODUCTS USEFUL IN CONNECTION THEREWITH Filed June 30, 1951 Suppori' Phofosensifive Elemeni' 10a lOb K {Phoi'osensifive Siiver H Halide Emulsion I Processing Agen'i Slripping Layer |5" Silver Precipii'ai'ing Layer Wa'l'erproof Subcoal' Su or? Receiving pp Si'rai'um Con'l'ainer Of Processing Ageni' (Prini' Receiving 'Elemenl' FIG. 2

Prini' Receiving Si'raium Sfripping Layer Abrasion Resis'larfi' Coal'ing il-ver Precipii'ai'ing Layer Wal'erproof 'subcoa'l' Supporl' FIG. 3

I INVENTOR ATTORNEYS United States Patent it. v

I PHOTOGRAPHIC SILVER HALIDE TRANSFER PROCESS AND THE PRINT-RECEIVING PROD 'UCTS USEFUL IN CONNECTION. THEREWITH Edwin H. Land, Cambridge; Mass., assignor to Polaroid Corporation, Cambridge, Mass;,' a corporation of Delaware Application June 30, 1951-; Serial No. 234,622

. 16 Claims. (CI; 96-29) This invention relates to :photographic 'products and processes and-smoreiparticularly to: silver -=halide-= transfer processes whereina. latent im'age in. a silver halide emulsion is developed and wherein soluble silver-complex obtained by reaction 'withtheaindeVel'oped silver lialide of :said emulsion is transferred from said emulsion and the .1 silver thereof isprecipitatedin another layer-to :form' a positive print, and to productsuseful-ms:print-receiving I elements in said processes.

It has heretofore been proposedto' formpositive prints .in a single 'stepby suitably treating a silver" halide-emulsion containing a latent image with a uniformly-applied layer of processing liquid. 3 In-one-form 'of this print making procedure, the processing liquid is in a viscous condition and. is spread in ailiquid film between'the photosensitiveelementcomprising'a silver halide emulsion and a print-receivingelementcomprising a suitable silver*pre cipitating layer.

It is oneobject'o f' the present?invention to'provide'improved products and processes "suitable for the performance of this type of transfer process whereby iithere'is' 'obtained as a result of the processing apositive'prinfwhich is dry immediately upon separation from thepho'tosensitive elementand" which gives noevidence asfar a'swetness is concerned of having beenin contactwith adiguid processing composition. In'accordance 'withthe present invention, the print-receiving element 'isl'so constructed that the viscous continuum of processing'agent separates therefrom and leaves no droplets or film of developing "composition'onthe print=receiving layer. 'Moreovergthe image-receiving stratum of the print receivingelementis thin, holding amass of water so small that thereis no tact'ual wetness and equilibrium with the environment. is

reached almost. immediately. Consequently, the print- "receiving sheet appears to the'observer to be a dry sheet .the instant it is peeled from'thenegativeelement which carries the viscous developer layer. It thus-becomes possible, inaccordance with the present invention, to achieve" the benefits which are ordinarily associated with'l liquid processes and yet to have a dry product immediately ,upon the completion of thetreatrnent thereof. The foregoing is accomplished by confiningthe permeabilityof the printreceivingelement to a very thin surfacestratum. Italso becomespossible by .virtue of this improvedstructure to obtain increased overall reliability in the .printformation -since amore..precise control vofthe Yfilmsprea'd between the, photosensitive element-.and .the print=receiving element is achieved.

Another .object is .-to .provide a: nove1 ,product .useful as a print reeeivinglelement..in-a.silver halidetransfer process in whichihe .processing .liquidisspread'in a thin viscous layer over the surfaceof said. element, said.prodnot being soconstructed as togive not only 'a dry-but also a curl-proof print at.the completion of the process. Bythe term .curl-,pro'of! is I meant proof againstthe. type 'of curling or "distortion"which.resultsfromthe differential effect o'f atmospheric conditions upon' "different layers of 5. :its layers.

2,823,122 iatented Feb. 11, 1958 "ice .JaI film. .zlt :has :heretofore 1 been 1the-:practice to provide :sp'ecial'xzoatings'tocompens'ate for. the -tendencyof a composite sheettocurl in'zresponselto the greater contraction :or expansion *of one ofitsilayers with respect 'to other of Byimakingl the print-receiving stratum as thin -.::as .it is .in the structureuof. the present inventiony this 'Ttendency to curl is: favloided, avoiding theuneed: for i the application of such special layers.

istillcanother:object is 'ito provide :a novel 'print receiv- .:ing.=.element ;having a: thin stratum adjacent one surface thereof which-includesazsilver precipitating.layerand in "'which the positive print is .formed,' said stratum being szseparated from the remainder'iof the print-receiving element by "alayer 'which is :substantially impervious 'to the processing liquid' used in the formation ofthe: transfer print and being provided with a surfacefrompwhich the viscous film of processing agent may be readily stripped. Other objects are' the-provision: of a novel silver halide transfer processausefuliwitha wide range of silver halide emulsions; inoludingpthehigh speed negative type -emulsionsfito givepositive transfer'prints of good quality-and stability and novel products capable of serving as printreceiving elements in the said process.

Other Qbjeets Ofthe invention will in" part be obvious -and will in part 'appear-hereinafter.

' 'The inventec'ot di'ngly comprises the several 'steps 1 and relationaif order 'of one or-more-of'suchstepswith respect to e'ach of' j otherspand the j product possessing the features, properties and the relation of 'elements' which are exemplified in the following detailed-disclosure, and

of one'form of print-receiving"'element'fupon.which'containers of the, processing 'agenttare"sopositionedas to be capable of distr'ibutingtheir contents between. the 'printreceiving element and "a photosensitive element; and

Fig. 3"is aview similar toFig. 1 o'fanother form of the print-receiving element of the invention.

The present invention comprehendsgimproved proc- "essesandproductsof the type whereby a'jpositive print is 'obtained'in asingle step by"suitably'ltreati ng a' silver halideemulsion containing a latent imagewith a uni- "form'lyapplied layer of processing liquid. 'ZThe processjin'g' liquid is'in a viscous condition 'aiidris spread in a Iliqui'd'film between the'photos'ensitive element comprising th'e' 'silver Jhalide emulsionan'd a print-receiving elementcomprising a suitable silver precipitating layer. The

liquid 'develops'the latent'image in the emulsion and "forms a s'olublesilver complex, e.;g., a 'thio'sulfate, with j undeveloped silver halide. This soluble silver complex is at least in parttrzinsported'iri the directionjdflheprintreceiving element and the silver thereof is largely precipitated in. the silver precipitating layer of said element to form apositive image in-silver. .To renderjtheprocess- :in composition viscous, a solid'Itliickening. agentLis ..dis persed therein. In onepr'eferred form o'ftheprocessing -composition, the thickening agentis athighemolecular weig'hfhlmdorming polymer.

1 "It hasibeen proposed. to .use,..in ,thezlformatiomof the .silver. transfer prints .by the foregoingprocess, certain.

compounds and elements whose presence during the process has a desirable effect on the amount and character of the silver precipitated during image formation. For this purpose, such materials as, for example, the metallic sulfides and selenides, the thiooxalates, the thioacetamides and others have been disclosed in my copending applications Serial No. 727,385, filed February 8, 1947, for Photographic Product and Process, now Patent No. 2,698,245, Serial No. 7,795, filed February 12, 1948,-for Photographic Process, now Patent No. 2,647,056, and Serial No. 164,908, filed May 29, 1950, for Photographic Silver Halide Transfer Product and Process, now abandoned. Other silver precipitating .agents have been proposed such, for example, as colloidal silver.

It has also been disclosed in my said copending applications that the precipitation and aggregation of silver obtained by using the silver precipitatingagents, including the above-mentioned materials, are very greatly improved by providing in the print-receiving element as a vehicle for said agents a macroscopically continuous matrix consisting essentially of submacroscopic agglomerates of particles of a water-insoluble, inorganic, chemically inert, adsorbent substance. Theword submacroscopic refers to a class of sizes which includes as a subclass those sizes known as submicroscopic. The substance preferably has a low coefficient ofabsorption for light as compared to silver and the matrix formed therefrom is essentially free of protective colloid action for silver. One example of such a matrix is a layer of silica such as is formed by'drying a layer of the hydrated colloidal silica dispersion available under the trade name Ludox or a layer of the dispersion of the silica aerogel available under the trade name Santocel C.

According to the present invention, the print-receiving element is constructed in a novel manner so that only a surface portion thereof, hereinafter characterized as the print-receiving stratum, is capable of being permeated to any appreciable extent by the ionic reagents contained in the liquid processing composition. The outer surface of this print-receiving stratum contacts the layer of processing composition and preferably this surface is so constituted as to have a lesser adhesion for the solid residue of the liquid processing composition than does the photosensitive element. As a result, the photosensitive element, when stripped from the print-receiving element, carries with it the residue of the processing composition. The entire print-receiving stratum may be essentially formed of a material having the desired stripping properties or preferably a thin film of a suitable stripping composition may constitute the outer surface portion of the print-receiving stratum, while the remainder of said print-receiving stratum is formed of a vehicle more suitable for carrying the silver precipitating agents. These silver precipitating agents for controlling and aggregating the silver precipitate that produces the positive image are dispersed throughout a part at least of the thickness of the print-receiving stratum. The remainder of the print-receiving element serves as a support for the printreceiving stratum and has contiguous to said stratum a surface which is substantially impervious to the liquid of the processing composition, which surface may be obtaine'dby having a liquid-impervious layer provided between the print-receiving stratum and a suitable supporting member for said stratum, or said liquid-impervious surface may be the surface portion of a supporting sheet which is entirely formed of liquid-impervious material.

As a result of this construction, such of the stainforming reactants as are retained by the print-receiving element after the formation of the positive print are primarily confined to the thin print-receiving stratum. In

general these reactants in their dissolved condition tend the layer of processing composition itself and so much of the thickness of the print-receiving element and the photosensitive element as is permeated by the processing composition. Because the print-receiving stratum constitutes such a small proportion of the total thickness of material permeated by the liquid, there is in effect a lesser mass of the undesirable stain-forming reactants in the print'receiving element than, would exist if a greater thickness of said element were penetrated by the liquid processing agent, Thus, the structure of the print-receiving element'is effective in minimizing, and, in some instances, making negligible some of the hazards to a finished print. These include the following: (l) the highlights of the print may turn yellow due to the oxidation of the unexhausted developing agent; (2) many oxidized developing agents may act as oxidizing agents for silver; hence, not only will the highlights turn yellow but the shadows will also fade; (3) the silver 'may be oxidized by other reagents as, for example, by sulfide from residual thiosulfate; and (4) the silver may be oxidized by oxidizing agents in the atmosphere.

As noted hereinabove, the print-receiving element has the viscous processing film stripped therefrom and the latter, because of its viscosity, leaves no droplets or film of developing composition upon the print-receiving element as it is stripped. Moreover, because of the thinness of the image-receiving stratum of the print-receiving element, said element holds an extremely small mass of water. Accordingly, as it is stripped, it comes at once into equilibrium with the environment and feels dry to the touch.

A further hazard to the print arises by virtue of this stripping of the processing agent in that the thin printreceiving stratum is ordinarily fairly readily susceptible to scratching and other surface abrasion effects. Provision is made in the-preferred form of the present invention for the protection of the print-receiving element such as sodium carboxymethyl cellulose.

against this hazard and this is accomplished without any substantial increase in the thickness of the print-receiving stratum.

The use of the novel products of the present invention 'in' the performance of the silver halide transfer process is illustrated diagrammatically in Fig. 1 wherein 10 represents a photosensitive element comprising a support 1011 and a photosensitive, silver halide emulsion layer 10b; 14 represents a layer of a relatively viscous processing compositioniand 12 is one embodiment of the novel print-receiving element of the invention in which the transfer print is formed.

Liquid layer 14 may be obtained by spreading the processing agent, for example, in a manner disclosed in my said copending application Serial No. 7,795, and the processing agent may be one of the fihn-fonning'processing agents disclosed in said copending application. It may comprise, for example, a developing agent such as hydroquinone, an alkali such as sodium hydroxide, a substance, such as sodium thios'ulfate, for forming a soluble silver complex with unexposed silver halide, and a high molecular weight film-forming thickening agent All these materials are preferably in aqueous solution and are preferably contained in the processing liquid prior to the spreading thereof as a layer 14. However, they may be in part or wholly added to the processing liquid as it is spreadbetween elements 10 and '12, being so located on or adjacent the surface of one or both of said elements as to be dissolved by or otherwise interacted with the liquid agent when thelatter wets said surface.

The'liquid processing composition may be provided for spreadingas a layer 14 between elements 10 and 12 by being contained in an elongated rupturable container 20 which, as shownin Fig. 2,'has a'length at least equal to'the transverse dimension of the area of photosensitive element '10 to which the liquid processing agent'isto be applied. One or more containers 20 may be attached factory as the inner lamina.

enemies 1 to one of elements and 12 and, inEig. 2;: two such containers are shown secured to the print-receiving sur- -face of element-1 2, being fspaced apart, lengthwise-bf i said element, afdistance equal'at'lea'st to-the length T of a single frame of the photosensitive element 10. Said elements 10 and" 12 may be connected together so that they can be superposed with the containers so positioned as to be capable of successively releasing their contents irr-a film betweensaid elements. Each of containers 20 is preferablylso 'constructedjas to be c'apable of retaining the liquidprocessing agent or composition therein for relatively long periods oftime without vapor loss or oxidation. oneex'ampiebt [suitable container of this type is formedfro'm a single 'mul'tilayefslieefofmaterial 'comprising' three'larninae. The'iniier lamina,"which provides the inner surface of thecontaine'r, is formed of a material which is'ch'emically inert-tothe reagents in the processing agent and which 'isimpervious to the liquid of the agent. Onecl'assbf materials" suitable forthis purpose, particularly where the processing "age'nfis' "an of a'strong, deformable,'relatively inexpensive sheet mate- 'rial'such as a'kraft paper. M I g The container 20 is preferably formed by taking the single sheet of'three-ply material and folding'thesame medially at 22, and thereafter securing the endmarginal "portions' '24 and the longitudinal marginal portions 26 of the two folded faces to one another, providing a central space or cavity 28 for containing'the processing liquid.

To fill-the container it is possible to-adhere together the opposite longitudinally"extending marginal portions '26 and one of the endmarginal'portions"24,the container being filled through the other end which is thereafter sealed.

Photosensitive element 10 may be any of the commercially available photosensitive silver halide films, the

term film as used herein being understood to include paper-backed emulsions. The products of the present 'i'nventionare particularly useful in improving'the results obtained when-thetransfer process-is carried out with one of thehigh-speed photosensitive silver halide emulsions such--asthe emulsion of the-relatively high-speed ortho- "--chromatic-filrns, -e.--g., Eastman Kodak 'Veric'hro'me film,

having an-ASAspeed rating of-OZOO and "an I ASA exposure index rating in the daylight of 50, and the extremely high-speed panchromatic emulsions, e. g.,- EastmanKodak Super XX'Pan haVing-an ASA speed rating of 0400 and an ASA exposure'index rating in the daylight of 100,'a'nd'Ansco Triple S Pan. Also satisfactory are the emulsions of Kodak Photofiure'safety films and Du Pont High Speed Pan film. The products and processes of the present'invention also give excellent results when used Withslower emulsions, for example,

the emulsions of Contrast Process Ortho film or the stripping layer a, which'constitutes the outer surface portion-thereof, and a silver precipitating layer 15b. Al-

though layers-lSa and 15b are preferably formedof different materials, they may, as noted hereinabove, be of the same single material with the silver precipitating iagentssuitablydispersed throughout at least aportion ief "the thickness "thereof. "Between 'the' 'print receiving 75 --soluble and stable salts of the above metals may befound,

prevent any appreciable penetrationbf the liquid therein "during the transferpro cess. IfsuPP'Ort '13 is substantialstratum '15 andthe support-13,-there,is showna waterimpermeable layer -or suBcoat 16.

. p as a cellulose ester, for example, "cellulose nitrate, cellulose acetate hutyrate, cellulose acetate or cellulose propionate.

If support 13iswater"permeable," layer 16co'ns'titutes a separate film of one of the water-impermeable"materials and is coated on. said support'im'suflicient "thickness vto ly' 'wa'ter 'impfermeableflayer 16 may be just anint'e'g'ral extension of said support, in'whichcase no' line of demarcatio'ns, assliown in Fi 1 actually existsbetweenflayer 16 and support 13. It is to'beclearlyunderstood; therefore, that-unless speeifically s'tated to the-contraryJaII future'meferences, especially inf-the claims, to a 'water impermeable layer and a supporttherefordoriot-preclude a structure whereir'i the layerand' support are integral parts of a single water irnperm'eable"sheetmaterial -such asa sheefbfone-df the aforementioned cellulose "esters.

"pervious'layer ltif that its primary purpose is to prevent any substantialpenetration of the liquid processing agent beyond print receivingstratum 15 during the performance of -thetransfer process and that in general the process f0r forming the 'po'sitiveprint takes less than five min- 'utes' -for its"c'ompl'etion {and more usually only about "one minute. "-Accordinglyythe water impermeability'of layer 16'-'neeel"'-only be such' as 'will prevent any penetr'ation 'o'f 'an aq'u'e'ous liquid' therethroughduring this time, and

the term water-impermeable, 'as 'used hereiriafter, in connection with layer 16, is to' be uiide'rstood 'as p'e'r taining wan im ermeabi-lity of' this ord'er. It may'- be desirable, in some instances, to provide layer l tif'with a furthenthin subcoat (not shown) forimp'roving' the ad- 'h'e'sion'between'between layer 16 and 'str'a'tu'm '15.-

"In'ge'ner-al, stratum 15 is at least permeab le tofthe print form'ing 5 components of an faqueous medrum and has dis'persedthroughout a portion at lea'st Lofthe ithi'ckness th'ereofa silver precipitating agentWhich may be --'any one of the materials' mentioned ifor this purpose' in imy above-noted applications but is preferably at leasthone of the relatively water-insoluble rnetallic lsulfidesfland selenides. The latterrt'erms are' 'to be understoodriasvineluding the polysulfidesand the poly'selenides within stheir scope. i Examples of :silver precipitating agents "-of "this preferred type are the 'so-call'ed' heavy metal "sulfides of zinc, chromium, gallium, iron, cadmium; cobalt; nickel, lead, antimony, bismuth; silver, cerium; arsenic, :copper and rhodium and the'selenides. of lead,- zinc;-antimony and nickel. 1.

-When using one or more of these heavymetal sulfides and 'selenides as :silver precipitating :agents'; it: is desirable to prevent the sulfide or selenide ions'of the crystals' of the precipitating agent from wandering ordiflusingduring the precipitation of silver. To accomplish this, there: is preferably dispersed throughout a portion at-ie'ast ofthe thickness of the print-receivingstratum:.-:15- atleast one metallic salt which is substantiallymore' soluble in the processing agent than the heavymetaL-sulfidemr;selenide used as the silver precipitating agentandwhich is irreducible'in the processing agent. This more soluble salt-has as its cation a metal whose ions form:sulfidesmfiselenides, as the case may be,-which -are difficultly soluble in lthe processing agent and which give up their sulfide or selenide ions to silveruby displacement. =-Aecordingly, when such' sulfide or "selenide ions are 'presentwthmmetal ions of the more soluble salt'ha've the e'fiect-ofimmediately precipitating the sulfide ions from-solution. Thesemore soluble or ion-capturing salts may bethe. salts of anywf the following metals cadmium, ceriumg(ous cobalt(ous) iron, lead, nickel,. manganese-and thorium. Satisfactory nickel and lead are preferred. erable to use the white or lightly colored salts, although for certain special purposes the more darkly colored salts can be employed.

It is also advantageous when using thesilve'r precipitat ing agents, and especially the metallic sulfides and selehides and colloidal silver, tosuitably aggregate the same and for this purpose a layer as previously described of silica orother granular, inorganic, water-insoluble, substantially chemically inert substance is preferably used. For certain photographic'purposes, as, for example, for documentduplication, a nongranular type. of dispersing .medium such as polyvinyl alcohol may be used for the silver precipitating agents.

One method of providing print-receiving layer 15b upon layer 16 is to form an aqueous dispersion of silica aerogel to which there is added a suitable quantity of one or more of the soluble ion-capturing salts. Thereafter, a substantially lesser molar quantity of a soluble sulfide, such as sodium sulfide, is added. The anions of sulfide and the cations of the ion-capturing salt combine to precipitate from the solution relatively insoluble crystals of the sulfide of the metal of 'the ion-capturing salt, thereby converting a portion of the latter to the sulfide. This produces a dispersion of the insoluble sulfide in the silica sol while leaving in solutionthe remainder of the ion-capturing salt; The concentration of'the latter in the initial solution in relation to the added amount of the soluble sulfide is such as to give in the final layer a substantially greater amount of the ion-capturing salt in proportion to the sulfide.

This dispersion comprising the sulfide in suspension and the ion-capturing salt in solution is thereafter roll-coated or otherwise applied as a layer upon the surface of layer 16 to give, upon drying, the silver precipitating layer 15b.

As hereinbefore noted, the layer of processing agent 14 is preferably spread in a viscous condition, for example, from a container 20, between the elements 10 and 12.. In order to impart to the liquid agent its desired viscosity, the liquid preferably contains in solution a water-soluble film-forming plastic'so that when the liquid is removed from the processing layer 14 by absorption and/or evaporation, there remains a solid plastic film.

For optimum stabilizing effects in the practice of the present invention, it is desirable that this film of plastic be stripped from the print-receiving element 12 after the is to minimize the adhesion between'the film-forming plastic in the processing agent and print-receiving element 12 so that upon separation of elements 10 and 12 the plastic film formed by the drying of processing layer 14 will adhere to photosensitive element 10 and will be stripped therewith from element'12. V

Stripping layer 15a may perform the additional function of providing an abrasion-resistant coating over the surface of the silica containing isilver precipitating layer 1511. Layer 15a may be, forv example, gum 'ar-a bic, cellulose acetate-hydrogen phthalate, polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, sodium 'alginate, pectin or polymethacrylic acid. It preferably has a thickness of the order of one to three microns. The above-mentioned plastics, suitable for coating 15a, are

especially useful for minimizing the adhesion between the film-forming plastic of layer 14 and stratum 15 when said film-forming-plastic of layer 14 is sodium carboxymethyl cellulose." It is important to note that the thickness of the stripping layer is approximately three microns or less and because of this his possible to use materials which in thicker vfilms 'would be relatively impervious during the processing'o'f the transfer print. Typical of such materials are the cellulosic esters and methacrylic esters. It is desirable when using these materials for stripping layer 15a to have the same in plasticized condition; whereas, when such materials are used to provide the liquid-impervioussub-coat 16, they are preferably in unplasticized condition.

, Where the permeable print-receiving stratum includes a stripping layer 151;, as above described, and the total thickness of said stratum is" small, being of the order of 6 microns or less, a remarkably dry print is obtained upon the separation of the print-receiving element 12 and the photosensitive element 10. The uniqueness of the phenomenonis evidenced especially by the fact that upon separation the surface of the photosensitive element 10 is perceptibly wet while the surface of the print-receiving element 12 is completely dry, the fihn of liquid which would ordinarily exist at the completion of a liquid treatment of the print having been totally removed from the I surface of said element 12 with the viscous processing agent. The relatively high viscosity of the processing agent serves to hold the liquid therein, and the layer .of processing agent, although in intimate contact with the print-receiving stratum and permitting the free transfer of ions and molecules thereto, relinquishes only a very small part of its liquid content to the print-receiving element. The mass of liquid which permeates print-receiving stratum 15 is so small that the sheet achieves an equilibrium with its environment almost instantaneously upon peeling. Accordingly, upon the separation of the said elements, element 12 is dry to the touch.

Examples of processes for forming a positive image wherein a silver halide transfer takes place and examples of the novel products of the invention when used as the print-receiving elements in the performance of said processes are given below, but it is expressly understood that these examples are merely illustrative and that the invention is not limited to the materials or proportions set out therein: 2

Example 1 A processing agent is prepared which comprises:

" Grams Water 1860 Sodium carboxymethyl cellulose 117 Sodium sulfite 78 Sodium hydroxide 74.6 Sodium thiosulfate 14.5 Citric acid 38.5 Hydroquinone 52 The processing agent is prepared by dissolving the sodium carboxymethyl cellulose, for example the commercially available Hercules #1362 medium viscosity type, in the water in a mixer at room temperature, and the solution is mixed therein for approximately one hour. Thereafter, the sodium sulfite, sodium hydroxide, sodium thiosulfate and citric acid are added to the solution, the addition being eifected in an inert atmosphere, for example of nitrogen. Upon dissolution of these materials, the hydroquinone is added and the solution is further mixed for an hour at approximately room temperature in a nonoxidizing atmosphere of nitrogen.

The novel print-receiving element 12 is formed by applying on the baryta-coated surface of a sheet of baryta paper a subcoat 16 consisting of unplasticized polyvinyl butyral, the latter being sufliciently water impermeable to prevent the penetration of liquid during the transfer process. Subcoat 16 is applied by rollcoating on support 13 a solution consisting of:

Polyvinyl butyral (unplasticized) grams 35 Isopropyl acetate cr 525 Methanol .....cc.....

Thereis-thenapplied to subcoat 16 the further layer 16b ofa thickness of 1 to 2 /2 microns by roll-coatingmnto said sub'coat thefollowingcomposition:

varies between 57% and 61% and which has a viscosity varying-between 1500 and 5000 c'entipoises. 'The surface of the print-receiving element -including layer 15b is thereafter dipped forapproximately thirty seconds "in a "solutionconsisting'of:

coatingthereon against a-smooth surface such; for ex-v ample, as }the polished surface of a metaldrum, a ,aqueous solution of polyvinyl alcohol in.- a-- layerwhich gives a.-po1yv-inyl alcohol coating -of-a thickness'of approximately: 1 to-2 /2- microns. Layers 15a and 15b together constitute the ;-print-receivingstratum of the.

present invention;

v-T he processing agent is spreadin' alayer 14-of-appro ximately =002-.003" in thickness between-the coated surface of element 12 andthe photosensitive silve'r-i lia'lide "emulsion "b of a photosensitive film 10. Emulsion 1012: is: a relatively --high'speed orthochromatic emiils'ion -li'ke the emulsion of Eastman Kodak'Verichrorne film, and has been exposed to predetermined"subjectmatter toformtherein a latent T image" of said subject 'matter,

"support 10a -forsaid emulsion being'a white paper. "The r lar'ninations formed by the' spreading of the proeessifig agent in a 1ayer-14'between 'element's' '10 =and=1'2 'is' k'ept -iintactfor approximately one-half to one =a'ndone half minutes; preferablyoneminute, and at the end 'of -this time element His-stripped from element"10. During the stripping-of the photosensitive element-10 from the -print-receivingelement 12, stripping layer 15a 'is' cleaved and this cleavage has the further effect of diminishing II the thickness of the print-receiving stratum 15 of the fin- -ished print,'thereby augmenting theadvantageous'effectsofi-a thin.print-receiving stratum hereinabove noted. -;Element-12, when so stripped, carries a positiveprint .zinwsilverof .the'subject matter of the latentfimage in e'mulsion 10b. The sodium carboxymethylcellulose of such other plastics as hydroxyethyl cellulose, polyvinyl "alcohol and the sodium salts of. polymethacrylic acid 'ahdpol'yacrylic acid may be used. The plastic is prefii -ably contained in the agent in sufiicient quantity'to yer-' 14-adher'es "to element 10. The print obtained in 10 impartqt'o 'the'compo'sitiona viscosityin excess of 1 ,000 centipoises at a temperature of approximately-24 C. Preferably, the viscosity of the processing agent is of th order of 1,000 to 2 00,000 centipoises at 24 C.

Other developing agents may-be'used, for example one of the following: 'p-aminophenol hydrochloride; bromohydroquinone; chlorohydroquinone; diaminophenol v "phenoldihydiochloride; toluhyhyl p aminophenol sulfate; arnixht of one-half "hydroq'u'ihone and a d;ai1damixture I hydroqiiinone and .hydr'oxyphenyla ino'efieti'c' "acid. e. soluble "silver complex, such other s 'iles a'S s odiurh"thioyaiiat, aim-- "mbjriiumt "66y e and ammonia may be em loyed.

.The 'vvaterpr'oof, subjebavls may, for e'xample,;be rontage;na htha-m1pmymeniacr nc acid or 'o'ne of .'thecelliilosic'iesters'isiieh as"celliilose nitrate, 'eellulose 2o aeif=ite,-ce1m16se Eu't'yfate of cellulose acetate prdpionate. Pfe fe rredhowev'er are-"the rubbery .type of plastics such a'sQpolyvihyliibiityral'.because such "materials are more enact in] eliminating Cracking of the print-receiving ."s'tratum which. might otherwise result from severe changes in atmospheric :conditions orrough handling of the print. stripping layef 5 1:541: may-be formed; for example, ofgum arabic, sodiurn alginate, pectin, cellulose acetate-hydrogen phthalatq;polyvinyl alcohol, hydroxyethyl cellulose or .polymethacrylic;aci'd and, when..-kept thin, may be of plastic ized'rnethylcellulose, ethylcellulose, methyl methacrylate or butylmethacrylate. It -is also preferable; in app1ying.:the print-receiving layer 15b; to the'waterp'roof subcoat 16, to use a suitable wetting agentsuch,--f'or example, as dibutylfiphenylplrenol sodiumdisulfon'ate, a sodium alkyl naphthalene -sulfonate- (e: g.= "Alk'anoh-B), ordecyl'b'enzene" sodium sulfonate. -Thi s" -is--prefe'r-ably --i-ntr oducedz irito' the 'composition' from--whichthe' silver ,.--pr-eeipitat-ing--layer :15 b -is' formedainr aratio ofe approximately'one'part -in fortyby volume. 4 9 I Example '2 A solution A is formed by mixing together:

Lead acetate grams v 0.2l

wan-mirth; 2.28

Fortlie'coating and dipping mixturesthat provide silver which is' eo'a'ted up'onthesubcoat 16to a thickness su'ch tliafthe s'olid' film' obtained therefrom is from 1' to3 micfoh's in thickness.

" Example .75 7 For the -icoating compositions whichrprovide 'fsilveif precipitating layer 15bof'Example 1, there is substituted the following: v

In another embodiment of the print-receiving element, as shown in Fig. 3, a layer 150 is provided'between stripping layer 15a and silver precipitating layer 15b, said layer 150 serving to improve the abrasion resistance of the silver precipitating layer and also to minimize the ionic penetration into layer 15b of certain of the components of theprocessing composition. Very satisfactory results are obtained with this arrangement when stripping layer 15a is selected from such of the materials noted above as being suitable for the stripping layer as are relatively soluble in an aqueous alkaline solution and layer 150 is a less soluble, although relatively permeable,.material. For example, satisfactory results have been obtained by forming stripping layer 15a from gum arabic and abrasion-resistant layer 150 from polyvinyl alcohol. Similar satisfactory results may be obtained by using two polymeric materials whose chemical structures are the same but whose molecular weights differ. For example, a low molecular weight.

1 formation of substantially grainless positive transparencies which are capable of being enlarged by projection to a substantial extent without appreciable loss in definition and in these transparencies it has been found satisfactory to eliminate the stripping layer of the above-described examples and to use a transparent cellulosic ester for support 13 so as to avoid the necessity for a separate waterproof subcoat 16.

Example One example of a print-receiving layer of this type comprises a .transparent support of cellulose acetate upon which has been directly coated a silver precipitating layer having the same composition as forms the layer 15b of Examples 1 through 4. In this form of the invention, it is preferable to omit not only the subcoat 16 but also the stripping layer 15a and to have the residue of the processing composition adhere to the print-receiving layer when the latter is stripped from the photosensitive element.

Because of the relative thinness of the silver precipitatingstratum'of the print-receiving element of the present invention, it is sometimes diflicult to incorporate within this thin permeable stratum a suflicient quantity of stabilizing agents to effect essentially complete stability. It

:has been found extremely efiective in order'to achieve stability to substitute for the sodium hydroxide of the processing composition of Example 1 a relatively volatile alkali, such as a volatile amine, e. g. diethyl amine. The effect of this substitution is to cause the alkali content of the print-receiving element to evaporate when the print receiving element is stripped from the photosensitive element, thereby producing a reduction of the alkalinity which tends to effectively stabilize the positive print.

In still another approach to the solution of this problem there is substituted for all or a substantial part of the relatively stain-forming hydroquinone of the composition of .Example 1 a reducing agent capable of functioning as a developer but which gives by-products that are substantially less stain-forming in character. An example of this type of reducing agent is ascorbic acid. Ascorbic acid is especially effective when used in combination with hydroquinone for it not only tends to supplement the developing action of hydroquinone but also serves as an antioxidant for the hydroquinone, reducing the oxidation of the latter in the print-receiving element and thus eifectively minimizing the formation of stains wh1ch would 1 affect the stability of the positive print.

Since certain changes may be made in the above product and process without departing from the scope of theinvention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic process for forming, by transfer, a print of a latent image contained in the silver halide layer of a photosensitive element, which process comprises the steps" of bringing a liquid processing composition into contact with said photosensitive element so that said layer is permeated with the liquid of said composition, providtaining a nonsiliceous silver precipitating agent, said printreceiving element being superposed on said photosensitive element with said silver precipitating stratum adjacent processing composition confined to said photosensitive said photosensitive element and with the liquid of said element and to said silver precipitating stratum, the surface of said support providing a barrier to the penetration of said liquid into said print-receiving element beyond said silver precipitating stratum, said liquid containing,

after permeation of the silver halide layer, reagents for developing exposed silver halide and for forming soluble complexes with undeveloped silver halide, maintaining said elements in their superposed relation without any appreciable penetration of said liquid into said support while said latent image is developed and until sufiicient silver is transferred as a complex to said print-receiving element to form a print, and stripping said print-receiving relement from said photosensitive element subsequent to said transfer, said silver precipitating stratum because of its thinness being substantially tactually dry as it is stripped from said photosensitive element.

'2. The process of claim 1 wherein the said reagents are contained in the processing composition before the latter is, applied to the photosensitive element.

3. A photographic process for forming, by transfer,

. a'print 'of a latent image contained in the silver halide emulsion of a photosensitive element, which process comprises the steps of spreading a liquid processing composition which contains a film-forming thickening agentbetween said photosensitive element and a print-receiving element,'said print-receiving element consisting of a supportand'a thin silver precipitating stratum, not exceeding 6 microns in thickness, coated on said support, the

surface of said support in contact with said stratum being 7 formed of an organic plastic impervious to the liquid of .said processing composition, said stratum containing a silver precipitating agent and comprising an inner layer ment and with the liquid of said processing composition confined to said photosensitive element and to said silver precipitating stratum, the surface of said support providing a barrier to the penetration of said liquid into said print-receiving element beyond said silver precipitating stratum, said liquid containing, after permeation of the silver halide emulsion, reagents, including a silver halide developer and a silver halide solvent, for developingthe latent i'magesilver halide and for forming solublesilver 'coinplexes'with undeveloped silver halide, maintaining said elements in their superposed relation without any appreciable penetration of said liquidinto said support ment and from the residual film ofsaid'thicke'ning' agent,

said silver precipitating stratum because of its thinness being substantially tactually dry as 'it isso stripped.

4. The process of claim 3 wherein the silver halide developer and "the silver h'alide"so1ve'nt are contained in the processing composition before"the latter 'is'spread between the elements. 7

5. The process of claim 3 wherein theliquidp'rocessing composition is spread from a c'ntaiiier mounted on one of said elements.

6. A photographic process for forming by transfer, a print of a latent image contained in the silver halide emulsion of a photosensitive element, which process comprises the steps of providing a layer of an aqueous liquid processing composition which contains a film-forming thickening agent between said photosensitive element and a print-receiving element, said print-receiving element consisting of a support and a silver precipitating stratum coated on said support, the surface of said support in contact with said stratum being formed of an organic, waterimpervious plastic, said stratum not exceeding 6 microns in thickness and comprising a matrix of inorganic, waterinsoluble, adsorbent particles having dispersed therethrough a lesser concentration of a silver precipitating agent chemically different from said matrix particles, said print-receiving element being superposed on said photosensitive element with said silver precipitating stratum adjacent said photosensitive element and with the liquid of said processing composition confined to said photosensitive element and to said silver precipitating stratum, the said surface of said support preventing penetration of said liquid into said print-receiving element beyond said silver precipitating stratum, said liquid containing, upon permeation of the silver halide emulsion, reagents, including a silver halide developer and a silver halide solvent, for developing the latent image silver halide and for forming soluble silver complexes with the undeveloped silver halide, maintaining said elements in their superposed relation without any appreciable penetration of said liquid into said support while said latent image is developed and until sufiicient silver is transferred to said silver precipitating stratum to form a print, and subsequent to said transfer stripping said print-receiving element from said photosensitive element and from the residual film of said thickening agent, said silver precipitating stratum because of its thinness being substantially tactually dry as it is so stripped.

7. The process of claim 6 wherein said matrix comprises particles of silica.

8. The process of claim 6 wherein the silver precipitating agent includes a substance from the class consisting of metallic sulfides, metallic selenides, thiooxalates, thioacetamides and colloidal silver.

9. A photographic process for forming, by transfer, a print of a latent image contained in the silver halide emulsion of a photosensitive element, which process comprises the steps of bringing an aqueous liquid processing composition into contact with said photosensitive element so that said emulsion is permeated with the liquid, providing a print-receiving element in superposed relation with said photosensitive element, said print-receiving element consisting of a support and a thin silver precipitating stratum coated on said support, the surface of said support in contact with said stratum being formed of an organic, water-impervious plastic, said stratum not exceeding 6 microns in thickness and comprising a matrix 1 of inorganic, 'ads'orbent; water-insoluble *parti'cl'es' con taining p articles of a silver *precipitat-ingagent chemically "different "from said-matrix: particles; saidprint-receiving element being superposed on said photosensitive element with said 'silverf preeipitatingstratum adjacent said photosensitive elemeiiuand 'with the "liquid of said. processing composition confinedrxto "said photosensitive element and to said silver precipitating"sfratumgthe surface 'of said support preventingthe pentratiomof sai'd liquid into said 'said"print-receiving element beyond 'said silver precipitating stratum, said liquid'-containing,'--upon" permeation'of the silver halide emulsion, reagents fordeveloping exposed silver halide and for forming soluble complexes with undeveloped silver halide, maintaining said elements in their superposed -relation "withput any appreciable penetration of said liquid into said support while said latent image is developed andfu "s'ufiicient silver is transferred'as a'corriplex to said t-receiving element to form 'a print, and'str gsaid'p t-receiving element from said photosensitive element subsequent to said'trans- "fer, said silver ptecipitati'rig"stratuin because "of its thinness being substantially tactually dry as it is stripped from said photosensitive element.

10. A photographic print-receiving element for having prints formed thereon by means of silver transfer from a photosensitive silver halide emulsion, said print-receiving element being substantially inert to visible light and con sisting of a support and a thin silver precipitating stratum coated upon said support, said silver precipitating stratum comprising an inner layer adjacent said support and an outer layer, said inner layer being formed principally of inorganic, adsorbent, water-insoluble particles which provide a matrix and particles of a silver precipitating agent, chemically difierent from said matrix particles, dispersed in said matrix in a concentration substantially lower than the concentration of said matrix particles, said outer layer being formed principally of organic plastic and being more abrasion resistant than said inner layer, said silver precipitating stratum having a total thickness not exceed ing 6 microns and being substantially pervious to an aqueous solution of soluble silver complex, said support having a water-impervious layer of organic plastic which provides the surface upon which said silver precipitating stratum is mounted.

11. The print-receiving element of claim 10 in which said adsorbent, water-insoluble particles are particles of silica.

12. The print-receiving element of claim 10 wherein said silver precipitating agent comprises at least one substance from the class consisting of metallic sulfides, metallic selenides, thiooxalates, thioacetamides and colloidal silver.

13. The print-receiving element of claim 10 wherein said support comprises a base of paper and said waterimpervious layer is a coating of organic plastic applied to said base.

14. A photographic print-receiving element for having prints formed thereon by means of silver transfer from a photosensitive silver halide emulsion, said print-receiving element being substantially inert to visible light and comprising a base layer, a water-impervious layer of organic plastic mounted on said base layer and a print-receiving, silver precipitating stratum not greater than 6 microns in thickness mounted directly on said water-impervious layer and providing an outer surface of said element, said printreceiving stratum comprising an inner layer formed principally of inorganic, adsorbent, water-insoluble particles constituting a matrix, particles of a silver precipitating agent, chemically diiferent from said matrix particles, being dispersed in said matrix in a concentration substantially lower than the concentration of said matrix particles, an intermediate layer formed principally of organic plastic and being more abrasion resistant than said inner layer, and an outer layer formed principally of organic plastic and being more water soluble than said intermediate layer.

15. The print-receiving element of claim 14 wherein said base is paper, said matrix particles are particles of a siliceous material and said outer layer comprises polyvinyl alcohol.

16. The print-receiving element of claim 14 which includes a container, said container holding a processing composition comprising a film-forming thickening agent capable of providing a residual, solid film when the composition is dried after spreading, said container being so mounted on the print-receiving element as to be able to dispense its contents over the surface of said silver precipitating stratum.

References Cited in the file of this patent UNITED STATES PATENTS 362,860 Thorp 'May 10, 1887 1,762,935 Sheppard et al June 10, 1930 1,971,430 Schneider Aug. 28, 1934 2,271,911 Bloch Sept. 5, '1939 2,280,986 Toland et va1. Apr. 28, 1942 18 2,296,636 'Hanahan Sept. 22, 1942 2,352,014 Rott June 10, 1944 2,433,515 Jahoda Dec. 30, 1947 2,543,181 Land Feb. 27, 1951 2,698,237 Land Dec. 28, 1954 FOREIGN PATENTS 3,736 Great Britain 1900 473,513 Great Britain Oct. 14, 1937 53,502 France July 16, 1945 S (2nd addition to No. 873,507) 59,365 Holland Apr. 17, 1947 OTHER REFERENCES Garneri, Photographic Notes, vol. 6, 'October 1861, page 280.

'Burmistrov,'The Photographic Journal, August 1936, vol. 60, pages 452-459.

Mees, The Theory of the Photographic Process, 1942,

20 pages 96'and 97. The ,Macmillan Co., N. Y. 

1. A PHOTOGRAPHIC PROCESS FOR FORMING, BY TRANSFER, A PRINT OF A LATENT IMAGE CONTAINED IN THE SILVER HALIDE LAYER OF A PHOTOSENSITIVE ELEMENT, WHICH PROCESS COMPRISES THE STEPS OF BRINGING A LIQUID PROCESSING COMPOSITION INTO CONTACT WITH SAID PHOTOSENSITIVE ELEMENT SO THAT SAID LAYER IS PERMEATED WITH THE LIQUID OF SAID COMPOSITION, PROVIDING A PRINT-RECEIVING ELEMENT IN SUPERPOSED RELATION WITH SAID PHOTOSENSITIVE ELEMENT, SAID PRINT-RECEIVING ELEMENT CONSISTING OF A SUPPORT AND A THIN SILVER PRECIPITATING STRATUM COATED ON SAID SUPPORT, THE SURFACE OF SAID SUPPORT IN CONTACT WITH SAID STRATUM BEING FORMED OF AN ORGANIC PLASTIC IMPREVIOUS TO THE LIQUID OF SAID PROCESSING COMPOSITION, SAID STRATUM NOT EXCEEDING 6 MICRONS IN THICKNESS AND COMPRISING A MATRIX OF SILICEOUS PARTICLES CON-TAINING A NONSILICEOUS SILVER PRECIPITATING AGENT, SAID PRINTRECEIVING ELEMENT BEING SUPERPOSED ON SAID PHOTOSENSITIVE ELEMENT WITH SAID SILVER PRECIPITATING STRATUM ADJACENT SAID PHOTOSENSITIVE ELEMENT AND WITH THE LIQUID OF SAID PROCESSING COMPOSITION CONFINED TO SAID PHOTOSENSITIVE ELEMENT AND TO SAID SILVER PRECIPITATING STRATUM, THE SURFACE OF SAID SUPPORT PROVIDING A BARRIER TO THE PENETRATION OF SAID LIQUID INTO SAID PRINT-RECEIVING ELEMENT BEYOND SAID SILVER PRECIPITAING STRATUM, SAID LIQUID CONTAINING, AFTER PERMEATION OF THE SILVER HALIDE LAYER, REAGENTS FOR DEVELOPING EXPOSED SILVER HALIDE AND FOR FORMING SOLUBLE COMPLEXES WITH UNDEVELOPED SILVER HALIDE, MAINTAINING SAID ELEMENTS IN THEIR SUPERPOSED RELATION WITHOUT ANY APPRECIABLE PENETRATION OF SAID LIQUID INTO SAID SUPPORT WHILE SAID LATENT IMAGE IS DEVELOPED AND UNTIL SUFFICIENT SILVER IS TRANSFERRED AS A COMPLEX TO SAID PRINT-RECEIVING ELEMENT TO FORM A PRINT, AND STRIPPING SAID PRINT-RECEIVING ELEMENT FROM SAID PHOTOSENSITIVE ELEMENT SUBSEQUENT TO SAID TRANSFER, SAID SILVER PRECIPITATING STRATUM BECAUSE OF ITS THINNESS BEING SUBSTANTIALLY TACTUALLY DRY AS IT IS STRIPPED FROM SAID PHOTOSENSITIVE ELEMENT. 